Hill hold for a vehicle

ABSTRACT

A vehicle hill hold may be accomplished, for a vehicle having an automated clutch between the engine output and the transmission input, while protecting the clutch from potential excess wear due to overheating. A hill hold may be accomplished by automatically switching the torque holding the vehicle in place from the clutch to the brakes. Alternatively, a hill hold may be accomplished by increasing an accelerator pedal position sensitivity and switching the clutch between fully engaged and fully disengaged based on changes in the pedal position.

BACKGROUND OF THE INVENTION

The present invention relates to clutches employed with vehicletransmissions, and more particularly to preventing overheating of suchclutches.

Dry clutches connected between the engine output and the transmissioninput are conventionally employed with vehicles having manualtransmissions. The engagement of these clutches are controlled by avehicle operator pressing on or releasing a clutch pedal. While theseconventional manual transmissions have some drawbacks relative toconventional automatic transmissions-the need for the vehicle operatorto actuate the clutch pedal and manually shift gears-they are stillemployed due to some inherent advantages. Namely, a conventional clutchand manual transmission is typically less expensive than a conventionalautomatic transmission and torque converter, and the conventional manualtransmission arrangement does not have the energy losses associated withthe torque converter.

Consequently, attempts have been made to develop a one or two clutch andmanual type of transmission arrangement that will operate like anautomatic transmission—an automated manual transmission or a powershifttransmission. That is, employ a vehicle controlled clutch and gearshifting system, but without a torque converter or the more complexplanetary gear sets and shift mechanisms of a conventional automatictransmission. One significant concern with these new systems, however,is the potential for heat build-up in the clutch while the vehicle is ina hill hold mode (i.e., the transmission is in a forward gear and thevehicle operator uses the accelerator pedal to maintain the vehicle at astand still on a hill). In order for the engine to be running while thevehicle is in gear and not moving, there must be slippage somewherealong the drive line. In the conventional automatic transmissionarrangement, the torque converter allows for this slippage by shearingthe fluid therein, with the torque converter readily having the thermalcapacity to absorb and dissipate the excess heat generated. But for anautomated type transmission with a clutch instead of a torque converter,the clutch will create the slippage, which creates heat build-up in theclutch. This heat build-up can occur relatively quickly, and canapproach temperatures that may cause significantly increased wear andpossibly damage the clutch.

To overcome the heat build-up concern, some have devised audible orvisual warning systems to alert the vehicle operator if the clutchtemperature is too high. But the vehicle operator may ignore thewarnings. Others have suggested the addition of one-way clutches orother transmission hardware to accomplish a hill hold function, butthese types of solutions add to the cost and complexity of thetransmission. Another suggested method for overcoming this concern is torapidly and automatically engage and disengage the clutch to cause thedrivetrain to pulsate in an attempt to encourage the vehicle operator torelease the accelerator pedal and actuate the brake pedal. However, suchpulsation being felt throughout the vehicle may cause concern for boththe vehicle operator and other occupants. Yet another suggested methodthat attempts to overcome this concern is one where, above a certaintemperature, the clutch will fully engage, thus causing the vehicle tomove forward and the vehicle operator to engage the brake pedal to stopthe forward movement. But this method may also cause a concern for thevehicle operator or vehicle occupants.

Thus, it is desirable to have an automated manual transmission with ahill hold function that prevents overheating of a clutch while avoidingmany of the drawbacks of the prior art.

SUMMARY OF INVENTION

An embodiment of the present invention contemplates a method ofperforming a hill hold on a vehicle having a clutch that selectivelyconnects an output of an engine to an input of a transmission. Themethod may comprise the steps of: detecting the vehicle is in a hillhold situation; automatically actuating at least one brake to increase abrake torque; and automatically actuating the clutch to decrease theclutch torque.

An embodiment of the present invention also contemplates a method ofperforming a hill hold on a vehicle having a clutch that selectivelyconnects an output of an engine to an input of a transmission. Themethod may comprise the steps of: detecting the vehicle is in a hillhold situation; automatically increasing an accelerator pedal positionsensitivity for an accelerator pedal in an electronic throttle controlsystem; detecting an increase or a decrease in a position of theaccelerator pedal; automatically fully engaging the clutch if theincrease in the position of the accelerator pedal is detected; andautomatically fully disengaging the clutch if the decrease in theposition of the accelerator pedal is detected.

An embodiment of the present invention also contemplates a vehicle thatmay comprise an engine having an electronically controlled throttle andan output, a transmission having an input, and a clutch having a clutchinput operatively engaging the output of the engine, a clutch outputoperatively engaging the input of the transmission, and a clutchactuator for selectively engaging the clutch input to the clutch output.The vehicle may also include an accelerator pedal having a pedalposition sensor, an antilock brake system, and a control unit incommunication with the clutch actuator, antilock brake system, pedalposition sensor and electronically controlled throttle, and including ahill hold clutch protector that detects when the vehicle is in a hillhold situation and actuates the antilock brake system to increase abrake torque while actuating the clutch actuator to decrease a clutchtorque.

An advantage of an embodiment of the present invention is that anautomated manual transmission may operate in a hill hold situation whileavoiding potential excessive wear or damage to the clutch.

Another advantage of an embodiment of the present invention is that themethod can be performed without requiring the addition of transmissionhardware to accomplish the hill hold function.

A further advantage of an embodiment of the present invention is thatthe hill hold function may be performed without creating potentialconcern to the vehicle operator. The protection of the clutch during ahill hold situation is accomplished without generating warning alerts tothe vehicle operator or causing the vehicle to pulsate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a portion of a vehicle powertrain inaccordance with an embodiment of the present invention.

FIG. 2 is a schematic diagram, similar to FIG. 1, but illustrating asecond embodiment of the present invention.

FIG. 3 is a flow chart disclosing a method of detecting a hill holdsituation in accordance with an embodiment of the present invention.

FIG. 4A is a flow chart disclosing a method of executing a hill holdclutch protection strategy in accordance with an embodiment of thepresent invention.

FIG. 4B is a flow chart similar to FIG. 3A, but illustrating a method ofexecuting a hill hold clutch protection strategy in accordance withanother embodiment of the present invention

DETAILED DESCRIPTION

FIG. 1 illustrates a portion of a vehicle 18, having a vehiclepowertrain 20 that includes an engine 22, with an electronicallycontrolled throttle 24 and an engine output shaft 26. The engine 22 maybe a conventional gasoline or diesel engine, or some other type ofengine if so desired. The output shaft 26 splits in two and is coupledto a first clutch 28 and a second clutch 30. The first and secondclutches 28, 30 are preferably dry clutches but may also be wet clutchesinstead, and may be located within a transmission 32 or adjacent to thetransmission 32. The transmission includes a transmission output shaft52 that connects to the rest of the powertrain 20, which may include adrive shaft 60, differential 62, axle 64, and wheels/tires 66. While theconfiguration appears generally as a rear wheel drive arrangement, thepresent invention is equally applicable to a front wheel drivearrangement as well.

The transmission 32 is preferably a type that has gear sets similar tothose of a conventional manual transmission rather than gear setssimilar to those of a conventional automatic transmission. Thetransmission 32 is also preferably configured as a powershifttransmission in which the odd numbered gear ratios—a first gear 36, athird gear 38, a fifth gear 40, and possibly a reverse gear 42—aredriven via an output 34 from the first clutch 28; and the even numberedgear ratios—a second gear 44, a fourth gear 46, and a sixth gear 48—aredriven via an output 50 from the second clutch 30. When the transmission32 is operating in one of the odd gears, the first clutch 28 is engagedand the second clutch 30 is disengaged, which allows for even numberedgear shifting. Then, the first clutch 28 is disengaged while the secondclutch 30 is engaged so the transmission 32 is now operating in one ofthe even numbered gears. Accordingly, this arrangement allows for torquedelivery through the transmission 32 to the transmission output shaft 52even during shifting. While the powertrain 20 employs a powershifttransmission 32, the present invention may also be applied to othertypes of transmissions, such as, for example, automated manualtransmissions, where clutch overheating during a hill hold situation maypresent a concern.

Through electronically controlled actuators, the engagement anddisengagement of the first and second clutches 28, 30, as well asshifting of the gears, is preferably automated. A first clutch actuator54 regulates the first clutch 28 and is electronically controlled by atransmission control unit 56, and a second clutch actuator 58 regulatesthe second clutch 30 and is also electronically controlled by thetransmission control unit 56. The dashed lines in FIGS. 1 and 2 indicateelectric or other types of communication between components. A firstgear actuator 68 manipulates the odd and reverse gears 36, 38, 40, 42,and a second gear actuator 70 manipulates the even gears 44, 46, 48,with both being controlled by the transmission control unit 56. Thetransmission control unit 56 also connects to a sensor 72 for detectingthe speed at the output of the transmission 32. The sensor 72 can beemployed for determining the speed of the vehicle, or, if so desired, adifferent sensor that forms part of an antilock brake or tractioncontrol system may be employed for determining the speed of the vehicle.The transmission control unit 56 is also in communication with an enginecontrol unit 74.

Alternatively, the transmission control unit 56 may be integral with theengine control unit 74.

The engine control unit 74 is also in communication with and controlsthe electronic throttle control 24 as well as a sensor 76 for detectingthe position or angle 86 of the accelerator pedal 78. And engine outputsensor 80 can detect the speed of the engine output shaft 26 and is alsoin communication with the engine control unit 74. An antilock brake andtraction control unit 82 also communicates with the engine control unit74. The antilock brake and traction control unit 82 is in communicationwith and controls vehicle brakes 84. The antilock brake and tractioncontrol unit 82 may have just antilock brake capabilities, just tractioncontrol capabilities or both, so long as automated control of the brakesis available. Also, while this control unit 82 is shown as separate fromthe engine control unit 74, it may also be integral therewith. Inaddition, while only two vehicle brakes 84 are illustrated, this systemis applicable to all four brakes on a vehicle. The engine control unit74 and antilock brake and traction control unit 82, as well as othersensors and subsystems to which they connect, will not be described inany detail herein since the design and functioning thereof are known tothose skilled in the art.

FIG. 2 illustrates a second embodiment of the present invention. Thisembodiment is similar to the first, but illustrates a differenttransmission arrangement and does not include an antilock brake ortraction control system. Accordingly, for elements in this embodimentthat are the same as the first embodiment, the same element number willbe used, but for elements that have changed, the element number willinclude an added prime. For the vehicle powertrain 20′, the engine 22,engine output shaft 26, driveshaft 60, differential 62, axle 64 andwheels/tires 66 may be the same as in the first embodiment. The brakes84′ are manually actuated by the driver depressing a brake pedal (notshown) but cannot be automatically actuated. The engine control unit 74′still communicates with the electronically controlled throttle 24,accelerator pedal position sensor 76, engine output sensor 80, andtransmission control unit 56′. The accelerator pedal position sensor 76again measures the position or angle 86 of the accelerator pedal 78.

The transmission control unit 56′ communicates with the clutch actuator54′, which regulates the clutch 28′, the transmission output sensor 72,and the gear actuator 68′, which manipulates the forward and reversegears 36′, 38′, 42′, 44′, 46′. The transmission 32′ illustrated in thissecond embodiment is an automated manual transmission rather than apowershift transmission as in the first embodiment, illustrating thatthe vehicle hill hold may be used with different types of transmissionsthat employ an automatically actuated clutch rather than a torqueconverter. Alternatively, if so desired, the vehicle 18′ may alsoinclude an antilock brake and/or traction control system, as illustratedin FIG. 1.

FIG. 3 is a flow chart illustrating a method of detecting whether a hillhold situation exists, and may be applied to either of the vehiclepowertrains 20, 20′ shown in FIGS. 1 and 2, respectively. The hill holdsituation is one where the vehicle is essentially at a standstill, in aforward or reverse gear, and the vehicle operator is maintaining thevehicle in this position by manipulating the accelerator pedal. Asmentioned above, it is important to detect this situation since theclutch slippage can cause the temperature of the clutch to rise rapidly.

A clutch threshold value is set, block 102. This clutch threshold valueis related to the estimated temperature (heat build-up) in the clutch.It may be a temperature or a time value and may be a look up table basedon empirical data or a mathematical model of heat transfer for theclutch. The estimation may include such factors as, for example, theinput energy due to the amount of slip and applied torque, coolingfactor based on the ability of the clutch to dissipate heat, and thethermal mass of the clutch. Or, as an alternative, the estimatedtemperature may be based on a temperature sensor.

With the vehicle in a forward or reverse gear, a determination is madeas to whether the velocity of the vehicle is approximately zero, block104. If not, then the vehicle is obviously not in a hill hold situation,so the routine starts over. If so, then the pedal position is comparedto a hill hold threshold, block 106. This pedal position threshold is anamount greater than zero but less than what would be deemed a demand bythe vehicle operator to launch the vehicle. Essentially a position in arange where the vehicle operator may be attempting to hold the vehiclein place by manipulation of the accelerator pedal. If the pedal positionis not above the hill hold threshold, then the routine starts over. Ifit is above the hill hold threshold, a determination is made as towhether the engine torque is greater than a predetermined minimum torquethreshold, block 108. If not, then the routine starts over. If it isabove the torque threshold, then a determination is made as to whetherthe pedal position is above a launch threshold, block 110. The launchthreshold is a pedal position above which would be deemed a demand bythe vehicle operator to launch the vehicle. If above this launchthreshold, then the routine jumps to execution of a vehicle launch,which is shown as block 218 in FIG. 4A (for a vehicle employing anantilock brake or traction control system for clutch protection) orblock 316 in FIG. 4B (for a vehicle that does not employ an antilockbrake or traction control system for clutch protection). If the pedalposition is not above the launch threshold, then the vehicle isdetermined to be in a hill hold mode.

A determination is now made as to whether the clutch threshold value isgreater than a predetermined limit, block 112. This predetermined limitwill be a time or a temperature value corresponding to the clutchthreshold value. For example, it may be a temperature of two hundred orthree hundred degrees Celsius, or an amount of time that the clutch hasbeen slipping. The predetermine limit is one where, above the limit, aconcern arises that the clutch may begin to experience undue wear orpossible damage due to heat build-up. If the clutch threshold is notabove the predetermined limit, then the clutch threshold value isincremented, block 114, and the steps are repeated to determine if thevehicle is still in a hill hold mode. The amount the threshold value isincremented relates to an estimated incremental increase in the heatbuild-up in the clutch as the vehicle remains in the hill hold mode. If,on the other hand, the clutch threshold is above the predeterminedlimit, then a hill hold clutch protection strategy is implemented, block116.

The hill hold clutch protection strategy implemented for a vehicledepends upon whether that vehicle has antilock brakes and/or tractioncontrol or not. For a vehicle with antilock brakes and/or tractioncontrol (that is, one where the brakes can be automatically actuated),the embodiment of the hill hold clutch protection strategy shown in FIG.4A is preferably employed. For a vehicle without antilock brakes ortraction control, the embodiment of the hill hold clutch protectionstrategy shown in FIG. 4B is employed. For example, a vehicle such asthat in FIG. 1 may employ the strategy of either FIG. 4A or 4B, althoughthe strategy of FIG. 4A is preferred, while a vehicle such as that inFIG. 2 will employ the strategy of FIG. 4B. Either way, these strategiesare applicable to both powershift and automated manual transmissionswhere a clutch or clutches are used in place of a torque converter.

For the hill hold clutch protection strategy shown in FIG. 4A, it beginswith ramping up the brake torque, block 200, and ramping down the clutchtorque, block 202. Preferably, the brake torque is ramped up somewhatfaster than the clutch torque is ramped down so that the vehiclemaintains its position on the hill without beginning to roll backwards.Optionally, while the clutch torque is ramped down, the engine controlsmay be correspondingly adjusted (such as, for example, via theelectronic throttle control) in order to maintain the engine speed,block 204. This will make the operation more transparent to the vehicleoperator, thus lessening the potential for the vehicle operator tobecome concerned as this strategy is carried out. A determination ismade as to whether the brakes are fully engaged and the clutch is fullydisengaged, block 206. If not, then blocks 200, 202 and 204 continuethis process. If they are, then, the clutch, being fully disengaged,will not build-up any more heat, while the brakes, being actuated, willhold the vehicle in place on the hill. All this is accomplished withoutrequiring any vehicle operator intervention or even requiring that thevehicle operator knows of the switch from clutch torque to brake torque.

The vehicle can now remain in this hill hold mode until the vehicleoperator initiates a change in the accelerator pedal position sufficientto indicate a desire to leave the hill hold mode. If the acceleratorpedal position is reduced by the vehicle operator to approximately zero,block 208, then the brake torque is ramped down, block 210. As the braketorque is ramped down, then, the vehicle can roll backwards on the hill.If the accelerator pedal position is increased above the vehicle launchthreshold, block 212, then the clutch torque is ramped up, block 214,while the brake torque is ramped down, block 216. In this situation,preferably the clutch torque is ramped up slightly faster than the braketorque is ramped down so the vehicle does not have a tendency to rollbackwards on the hill during the transition. The vehicle launchstrategy, block 218, can then be executed. The particular strategyemployed for controlling the engine, clutch and transmission shiftingduring the execution of the vehicle launch does not form a part of theinvention herein and so will not be discussed further.

For the hill hold clutch protection strategy shown in FIG. 4B, it beginswith increasing the pedal position sensitivity, block 300. Adetermination is made whether the pedal position is now greater than thelaunch threshold, which, as discussed above, is a pedal position abovewhich would be deemed a demand by the vehicle operator to launch thevehicle. If above this launch threshold, then the pedal positionsensitivity is reset to its normal level, block 314, and a vehiclelaunch is executed, block 316.

If the pedal position is not greater than the launch threshold, then adetermination is made as to whether the pedal position has increased,block 304. Since the pedal position sensitivity has been increased, thepedal position increase may be a relatively small movement and still bedetected as an increase. If a pedal position increase is detected, thenthe clutch is fully engaged, block 306. If there is no increase, adetermination is made whether the pedal position is decreased, block308. Again, since the sensitivity of the pedal position has beenincreased, even a small movement may be detected. If there is nodecrease in the pedal position, then the pedal position sensitivity isincreased again, and a check is made for an increase or decrease in thepedal position. If a decrease in the pedal position is detected, thenthe clutch is fully disengaged, block 310. If the pedal position is nowabout zero, block 312, then the vehicle operator has likely switched tothe brake to hold the vehicle in place, so the clutch remainsdisengaged, block 318. If not zero, then the pedal position sensitivityis increased again and checks for increase or decrease in pedal positionare made again. Alternatively, the pedal position sensitivity may beincreased more significantly the first time, without incrementalincreases later. The pedal position checks, then, would repeatedly occurwithout incrementally increasing the pedal position sensitivity betweenchecks.

Since, with this process, the clutch is generally completely engaged ordisengaged—rather than in a continuous state of slipping—the amount ofheat building-up in the clutch should be greatly reduced. Moreover, theincreased sensitivity of the accelerator pedal may discourage the driverfrom employing the accelerator pedal as a means for maintaining thevehicle on a hill. The process makes it extremely difficult for thevehicle operator to hold the vehicle steady on a hill by manipulation ofthe accelerator pedal alone. After a few cycles with the increased pedalposition sensitivity, the vehicle operator will most likely remove hisfoot from the accelerator pedal and use the most appropriate device tohold the vehicle on a hill—the brake.

Yet, despite the increase in pedal position sensitivity and switchingbetween full engagement and full disengagement of the clutch, thisprocess still leaves the vehicle operator in control of the vehicle.Thus, the concerns that may arise for a vehicle operator with some priorart systems are eliminated.

While certain embodiments of the present invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

1. A method of performing a hill hold on a vehicle having a clutch thatselectively connects an output of an engine to an input of atransmission, the method comprising the steps of: (a) detecting thevehicle is in a hill hold situation; (b) automatically actuating atleast one brake to increase a brake torque; and (c) automaticallyactuating the clutch to decrease the clutch torque.
 2. The method ofclaim 1 wherein steps (b) and (c) are further defined by the increase inbrake torque occurring substantially simultaneously with the decrease inthe clutch torque, and the increase in brake torque being initiallygreater than the decrease in the clutch torque.
 3. The method of claim 2further including: after step (a), waiting a predetermined time beforeexecuting steps (b) and (c).
 4. The method of claim 2 further including:after step (a), estimating a clutch temperature, and waiting until theestimated clutch temperature exceeds a predetermined limit beforeexecuting steps (b) and (c).
 5. The method of claim 1 further including:after step (a), waiting a predetermined time before executing steps (b)and (c).
 6. The method of claim 1 further including: after step (a),estimating a clutch temperature, and waiting until the estimated clutchtemperature exceeds a predetermined limit before executing steps (b) and(c).
 7. The method of claim 1 wherein step (a) is further defined by avelocity of the vehicle being zero, a position of an accelerator pedalbeing greater than a predetermined pedal position threshold, and anengine torque being greater than a predetermined torque threshold. 8.The method of claim 1 further including the steps of: (d) detecting aposition of an accelerator pedal to be greater than a predeterminedvehicle launch pedal position; (e) automatically actuating the clutch toincrease the clutch torque; and (f) automatically actuating the at leastone brake to decrease the brake torque.
 9. The method of claim 8 whereinsteps (e) and (f) are further defined by the increase in clutch torqueoccurring substantially simultaneously with the decrease in the braketorque, and the increase in clutch torque being initially greater thanthe decrease in the brake torque.
 10. The method of claim 1 wherein step(b) is further defined by activating an antilock brake system toautomatically actuating the at least one brake.
 11. The method of claim1 further including the step of: (d) adjusting the engine whileperforming step (c) to maintain a generally constant engine speed duringthe automated actuation of the clutch.
 12. A method of performing a hillhold on a vehicle having a clutch that selectively connects an output ofan engine to an input of a transmission, the method comprising the stepsof: (a) detecting the vehicle is in a hill hold situation; (b)automatically increasing an accelerator pedal position sensitivity foran accelerator pedal in an electronic throttle control system; (c)detecting an increase or a decrease in a position of the acceleratorpedal; (d) automatically fully engaging the clutch if the increase inthe position of the accelerator pedal is detected; and (e) automaticallyfully disengaging the clutch if the decrease in the position of theaccelerator pedal is detected.
 13. The method of claim 12 furtherincluding: after step (a), waiting a predetermined time before executingstep (b).
 14. The method of claim 12 further including: after step (a),estimating a clutch temperature, and waiting until the estimated clutchtemperature exceeds a predetermined limit before executing step (b). 15.The method of claim 14 wherein step (a) is further defined by a velocityof the vehicle being zero, a position of the accelerator pedal beinggreater than a predetermined pedal position threshold, and an enginetorque being greater than a predetermined torque threshold.
 16. Themethod of claim 12 wherein step (a) is further defined by a velocity ofthe vehicle being zero, a position of the accelerator pedal beinggreater than a predetermined pedal position threshold, and an enginetorque being greater than a predetermined torque threshold.
 17. Themethod of claim 12 further including the steps of: (f) detecting theposition of the accelerator pedal to be greater than a predeterminedvehicle launch pedal position; (g) reducing the pedal positionsensitivity to an initial pedal position sensitivity; and (h)automatically engaging the clutch if the clutch is disengaged when step(f) occurs.
 18. A vehicle comprising: an engine having an electronicallycontrolled throftle and an output; a transmission having an input; aclutch having a clutch input operatively engaging the output of theengine, a clutch output operatively engaging the input of thetransmission, and a clutch actuator for selectively engaging the clutchinput to the clutch output; an accelerator pedal having a pedal positionsensor; an antilock brake system; and a control unit in communicationwith the clutch actuator, antilock brake system, pedal position sensorand electronically controlled throttle, and including a hill hold clutchprotector that detects when the vehicle is in a hill hold situation andactuates the antilock brake system to increase a brake torque whileactuating the clutch actuator to decrease a clutch torque.
 19. Thevehicle of claim 18 wherein the transmission is a powershifttransmission.
 20. The vehicle of claim 18 wherein the clutch is a dryclutch.